Usually the flights from Manchester and Gatwick are on one of 5 aircraft:
<TABLE><TBODY><TR><TD class=moreinfo></TD><TD class=moreinfo></TD><TD class=moreinfo></TD></TR><TR><TD class=fieldTD>
G-VGAL</TD><TD class=fieldTD>747-443</TD><TD class=fieldTD>Jersey Girl</TD></TR><TR><TD class=fieldTD>
G-VLIP</TD><TD class=fieldTD>747-443</TD><TD class=fieldTD>Hot Lips</TD></TR><TR><TD class=fieldTD>
G-VROM</TD><TD class=fieldTD>747-443</TD><TD class=fieldTD>Barbarella</TD></TR><TR><TD class=fieldTD>
G-VROS</TD><TD class=fieldTD>747-443</TD><TD class=fieldTD>English Rose</TD></TR><TR><TD class=fieldTD>
G-VROY</TD><TD class=fieldTD>747-443</TD><TD class=fieldTD>Pretty Woman</TD></TR></TBODY></TABLE>
You can check seat configurations here:
http://www.v-flyer.com/seatmaps.asp
31a and 33a are both over the wing - 33 seems to share a window.
I think on Seat Guru you should look at 747-400 vers. 2 or 3
Having said that, every now and again you may get a different aircraft due to operational reasons.